The invention relates generally to photo lithography, and more particularly, to a system for performing lithography on two and three dimensional substrates such as a spherical shaped substrate.
Conventional integrated circuits, or xe2x80x9cchips,xe2x80x9d are formed from two dimensional or flat surface semiconductor wafers. The semiconductor wafer is first manufactured in a semiconductor material manufacturing facility and is then provided to a fabrication facility. At the latter facility, several layers are processed onto the semiconductor wafer surface using various design concepts, such as VLSI design. Although the processed chip includes several layers fabricated thereon, the chip still remains relatively flat.
U.S. Pat. No. 5,955,776, which is hereby incorporated by reference, describes a three dimensional, spherical-shaped substrate for receiving various circuits. Of the many process disclosed in the above-referenced application, several are related to imaging a circuit design onto the three dimensional substrate. Often, the circuit design to be imaged may be two dimensional in nature.
There are numerous problems associated with imaging a two-dimensional circuit design onto a three-dimensional substrate, such as a spherical shaped substrate. For example, converting two-dimensional computer aided designs (CAD) of a circuit into a mask for projecting onto a three-dimensional surface requires separation of the circuit into unit segments that can be positioned on the mask and then projected onto the device. Thus, when designing two-dimensional integrated circuits (IC) using CAD tools, there must be a way to segment the design into sections that can be positioned on a mask and projected onto a three-dimensional surface. Also, it is very difficult to expose all surfaces of a three-dimensional substrate.
One partial solution is shown in U.S. Pat. Ser. No. 09/351,203. This application teaches a system for designing a flat mask to be imaged onto a spherical substrate. The system uses a mask and several angled mirrors for reflecting a pattern from the mask onto various portions of the substrate. However, this solution has poor light efficiency due to the mask and the angled mirrors.
Another partial solution is shown in U.S. Pat. No. 5,691,541. This patent teaches a maskless, reticle-free lithography system. However, this solution is for static systems, limited to two-dimensional substrates, and does not dynamically provide fine pattern alignment.
These and other conventional solutions do not provide the accuracy and light intensity often required for performing lithography on a three dimensional substrate. Therefore, what is still needed is a system and method for projecting a two-dimensional circuit design onto a three dimensional substrate.
A technological advance is achieved by a method, system, and lense system for performing lithography on a substrate. In one embodiment, the method captures the substrate and divides it into a number of regions. The substrate is first rough-aligned, and then a fine-alignment offset is determined. A pattern is then projected onto a first region of the substrate, adjusted by the first fine-alignment offset.
In some embodiments, the method then re-captures the substrate and fine-aligns a second pattern. The second pattern is then projected onto a second region of the substrate.
In some embodiments, the fine-alignment is performed by receiving an image of the roughly aligned substrate and comparing a predetermined mark on the image with the first pattern. This comparison can thereby determine the fine-alignment offset.
In some embodiments, the pattern is digitally stored in a computer memory device so that fine-aligning can be accomplished by moving the pattern in memory.
In one embodiment, the system for performing lithography on a substrate includes a lense section having one or more lenses, two light sources, and a device for projecting and exposing the pattern through the lense section and onto the substrate. Light from the first light source is used for exposing the pattern while light from second light source is used for providing an alignment image. An image sensor receives the alignment image from the substrate and uses it to properly align the pattern to the substrate.
In some embodiments, the system includes a beam splitter for separately directing the first and second lights. The beam splitter can separately direct the second light coming from the second light source and the alignment image coming from the substrate.
In another embodiment, the system utilizes a single source of light. A device such as a digital imaging device converts the light into a pattern, projects the pattern through the lense section, and exposes the pattern onto the substrate. A beam splitter is positioned between the digital imaging device and the substrate for separately directing an image of the substrate to an image sensor. As a result, the substrate image is used to accommodate the projection of the pattern onto the substrate so that the pattern is properly aligned to the substrate.
In some embodiments, the system includes a computer for receiving the alignment image from the image sensor and modifying the pattern used by the device to align the pattern with the substrate. The pattern may be digital so that the computer modifies the digital pattern by moving the pattern in memory.
In some embodiments, the system utilizes a reservoir for containing a transparent fluid through which the light may travel before reaching the substrate. One or more lenses of the lense section may be located in the reservoir of transparent fluid and/or may be part of the reservoir. In addition, a second reservoir may be used to contain the substrate.
In some embodiments, the system may use multiple lense sections and light sources. These embodiments may simultaneously expose different regions of the substrate, or may sequentially expose the substrate after it moves from one holder to another.
In one embodiment, a unique lense system can be used for nonplanar substrates. The lense system includes a first lense section for receiving a pattern and producing a concave image of the pattern. The concave image can then be received by a second lense section for producing a nonplanar image of the pattern. The nonplanar image coincides with the nonplanar substrate.